wrightwing wrote:The F-22 and F-35 are optimized for different speed ranges.

Yes, I just wonder if the DSI tech was mature back then or not. Is DSI less favorable for supercruise well above M1?

Rhoads

In other words, the inlet designs used in the F-22 and F-35 differ, due to the speed range that they're optimized for, not due to available technology. The F-22's super cruise speeds are near the max limits of DSI, and its top speed exceeds those limits.

Makes sense. But it seems there are differing ideas. Some are saying the DSI tech just wasn't mature when the F-22 was under development and you're saying the contrary and that it purely has to do with speed. Can you discuss why the DSI does not perform well at the F-22 supercruise speeds? Couldnt one design a specialized DSI for higher mach numbers?

1. The YF-22 was designed 1984-88 with the present inlet configuration.2. The F-22 FSD started in late 1991.3. GD/Fort Worth joined Lockheed in 1993.4. The GD/Fort Worth development work on DSI was between 1990 to 1996, and DSI was chosen for JAST.5. JAST program was between 1994-1997 with the down-select of Lockheed and Boeing to go forward in 1997.6. Northrop and BAE that were in the McAir losing JAST team joined the down-selected Lockheed team to go-on for JSF program.7. Lockheed Martin was formed with the addition of Martin Marietta & others in 1997.8. Boeing bought McAir & Rockwell in 1998 and joined forces for JSF competition.9. LM Aero-Northrop/Grummann-BAE team beat Boeing for JSF in 2001 after flyoff.

It is obvious that DSI was not in anyone's mind in the 1980's. LM Aero considered using DSI to only meet JSF/F-35 performance requirements. Whether DSI is suitable for the super-cruising requirements of ATF will be a very complex question at this stage of the game.

Your time line is very clear, but remember GD/Fort Worth was a 1/3 partner along with Boeing and Lockheed in the YF-22 and F-22 programs. F-22 FSD could have benefited from DSI development work at GDFW. All of which makes me guess lack of DSI on F-22 was a performance decision, not a technology decision.

The F-22 FSD contract award was in the Fall of 1991, and the first flight of the development aircraft was scheduled and executed in 1996. It would a stretch and be very risky to decide on a major inlet change when the DSI development work was just underway simultaneously.

In addition, the F-22 teaming agreement was a rather strange animal in that every major system on the aircraft was assigned a lead team member and the other two team members only have support engineering roles. Therefore, the team lead actually had major say so on the final design of the system. Interesting enough, even though GD/Fort Worth was assigned the mid-fuselage including 95% of the inlet duct for design and fabrication, the inlet lip region actually was assigned to Lockheed Marietta and was considered to be a part of the forward fuselage.

Whether DSI was ever being considered by the F-22 FSD team will be anyone's guess. Personally, it is doubtful.

The J-20's DSI bump always looked a bit weird to me, since it almost seems like the bump isn't quite large enough to properly divert that boundary layer. But then again, these are things that's hard to eyeball, and maybe CFD and windtunnel testing showed that it's enough.

On the other hand, having porous plates on the DSI bump of the JF-17 seems to defeat the purpose of a DSI in the first place.

scat wrote:The F-22 FSD contract award was in the Fall of 1991, and the first flight of the development aircraft was scheduled and executed in 1996. It would a stretch and be very risky to decide on a major inlet change when the DSI development work was just underway simultaneously.

In addition, the F-22 teaming agreement was a rather strange animal in that every major system on the aircraft was assigned a lead team member and the other two team members only have support engineering roles. Therefore, the team lead actually had major say so on the final design of the system. Interesting enough, even though GD/Fort Worth was assigned the mid-fuselage including 95% of the inlet duct for design and fabrication, the inlet lip region actually was assigned to Lockheed Marietta and was considered to be a part of the forward fuselage.

Whether DSI was ever being considered by the F-22 FSD team will be anyone's guess. Personally, it is doubtful.

Interestingly, based on drawings of the EMD F-23, it seems like it would've had a DSI bump as well.

A few years back, I was surprised to find the attached close-in photo of the J-17 DSI. In this case, bleed air holes were observed to be quite extensive both inside and outside of the inlet cowl. In fact, they were densely populated behind the DSI bump. If the DSI was designed properly, no bleed-air holes or porous plates is necessary as in the F-35 inlet.

That was the reason that I asked whether anyone came across a close-in shot of the J-20 inlet because its DSI also appeared to be funky...small as compared to the size of the inlet and asymmetrically located closed to the top of the inlet. a close-in image will reveil whether bleed air holes are also necessary for J-20. If so, the Chengdu design team must have a different design philosophy on the DSI. I just do not understand why the porous plate is necessary at all.

From what I can tell, the J-20 inlet doesn't seem to have porous plates around the DSI bump, but there's a porous hexagonal grid on the outside of the cowl right behind the intake. The F-22 also has porous plates right behind the intake inside the inlet.

As stated in my original post, the DSI development at GD/FW and the subsequent application on the F-35 were a direct result of the experience with the F-22 inlet. The prime objective was to eliminate most of the standard subsystems necessary to divert the boundary layer air away from the inlet and to prevent ingestion into the engine. These subsystems included the diverter, bleed air holes (porous plates), and pipes/doors, etc were heavy and complex to manufacture. The F-35 design was successful in the total elimination of these standard items while meeting the propulsion requirement of the aircraft.

Since the propulsion requirements of the F-22 are different, one must initiate an extensive study whether it is possible to do the same for F-22. This statement may also apply to the Chengdu fighters as well. Nonetheless, we are here to observe and discuss the differences of their DSI configurations from the F-35.

Makes sense. But it seems there are differing ideas. Some are saying the DSI tech just wasn't mature when the F-22 was under development and you're saying the contrary and that it purely has to do with speed. Can you discuss why the DSI does not perform well at the F-22 supercruise speeds? Couldnt one design a specialized DSI for higher mach numbers?

It's not either/or, but inlet designs are largely based around specifications, as well as technology. Using DSI inlets would likely result in a lower top speed, for the F-22, than the design that was chosen. The F-35 was designed around a M.95 to M1.6 range. The F-22 supercruises faster than the F-35's maximum speed, and has a top speed in the M2.2 to 2.4 region. It's much more difficult to get >M2 with DSI inlets.

As others have pointed out, the performance specs for the F-22 require a dedicated type of intake design. Given the fact that the F-22 was designed more for high altitude high speed flight wouldn't a DSI disrupt the airflow leading into the intake? From my understanding shock cones were movable structures to better regulate the super sonic shock cones and air into the intake thus leading to better high speed performance. If that is the case wouldn't the fixed position of the DSI hurt the F-22's high speed performance? How the F-22 with its S-Shaped inlet ducts is able to achieve supercruise of mach 1.5 and greater still blows me away.

Makes sense. But it seems there are differing ideas. Some are saying the DSI tech just wasn't mature when the F-22 was under development and you're saying the contrary and that it purely has to do with speed. Can you discuss why the DSI does not perform well at the F-22 supercruise speeds? Couldnt one design a specialized DSI for higher mach numbers?

It's not either/or, but inlet designs are largely based around specifications, as well as technology. Using DSI inlets would likely result in a lower top speed, for the F-22, than the design that was chosen. The F-35 was designed around a M.95 to M1.6 range. The F-22 supercruises faster than the F-35's maximum speed, and has a top speed in the M2.2 to 2.4 region. It's much more difficult to get >M2 with DSI inlets.

This makes sense wrightwing. I guess I need to do further research to understand how the DSI works and why it's impractical for high-mach flight. Part of my question, looking back on it, was based on the fact that modern Chinese fighters, specifically the J-20, use DSI and have a similar combat role to the F-22. Hence my curiosity.